Study On Particle Size Distribution Characteristics Of High Temperature FLiBe And FLiBeZr Molten Salt

As fuel salt carrier of thorium molten salt reactor project,FLiBe molten salt will melt and evaporate a large amount of steam at high temperature.After cooling,molten salt vapor condenses to form molten salt particles,which enter off gas treatment device with argon purge.Due to its toxicity,these beryllium-containing particles need accurate monitoring,efficient removal and allowable discharge.Particle size distribution(PSD)is the key to solve these problems.In this paper,particle size distribution characteristics of high temperature FLiBe and FLiBeZr molten salt particles are studied.Based on vacuum distillation apparatus of molten salt and low pressure impact sampler,an experimental platform is built to investigate the particle size distribution of high temperature molten salt.In terms of temperature setting,sample collection,sample treatment and testing,a unified and reasonable experimental procedure and operation standard has been gradually explored,which lays a foundation for subsequent analysis and comparison of experimental results.The experimental temperature,air pressure,sampling time and salt used in the experiment can be adjusted according to experimental requirements.It is found that the particle size distribution of FLiBe molten salt particles is in the range of more than 2.5μm at room temperature in longtime suspending,while instantaneous sampling at high temperature is in the range of 0.26-2.5μm.Gas purging and sampling time at high temperature affect the concentration of molten salt particles,but have no obvious effect on particle size distribution.With the increase of temperature,the particle concentration increases rapidly,the peak particle size stabilizes in the large particle size range of 2.5μm,particles are more concentrated.With the increase of temperature,the mass concentration of beryllium particles of FLiBeZr molten salt increases,and the peak particle size is stable in the large particle segment around 4.4μm.The particle size distribution of the two kinds of molten salt is unimodal.With the increase of temperature,beryllium mass concentration increases,and sampling amount increases,and the peak particle size of the two kinds of molten salt is in the large particle size range.Scanning electron microscope results show that the molten salt particles of FLiBe are regular spherical rather than crystalline,indicating that the growth of molten salt particles may be caused by collision deposition.SEM results of FLiBeZr molten salt particles show that the large particles are mainly single particles,while the small particles are mainly agglomerated and adsorbed.The smaller the particle size is,the bigger the number of particles is.The phenomenon of hygroscopic hydrolysis of very fine particles is similar to salt.